![]() ![]() According to the occurrence rate of rocky planets orbiting solar-type stars, 4 approximately 50 Earth-like planets or super Earths will be detected by observing 100 FGK stars during the mission.ĬHES will provide the first direct measurements of the true masses and inclinations of Earth twins and super Earths orbiting our neighboring stars based on micro-arcsecond relative astrometry from space. The satellite is designed to have a lifespan of 5 years, during which time all target stars will be extensively observed. The mission orbit of the CHES satellite will move about the L2 point of the sun and Earth. Heterodyne laser interferometric calibration technology is employed to ensure micro-arcsecond-level astrometric precision, 3 which is required to detect habitable-zone Earth twins orbiting nearby stars. ![]() The on-board calibration subsystem consists of a metrology assembly. The camera focal plane is composed of 81 MOSAIC scientific CMOS detectors, each with 4 K × 4 K pixels. The optical subsystem is a coaxial three-mirror anastigmat with a 1.2 m aperture, 0.44° × 0.44° field of view, and 500–900 nm waveband. The scientific payload is a high-quality, low-distortion, high-stability telescope with an optical subsystem, camera subsystem, and on-board calibration subsystem. The subtle change reflects the very tiny wobble of the target star caused by its orbiting planet’s gravitational perturbances and reveals terrestrial planets in the habitable zones of nearby solar-type stars with real masses and three-dimensional orbits. For an Earth twin orbiting at 1 AU around a solar-type star at a distance of 10 pc, the astrometry wobble from the host star induced by the Earth twin is estimated to be roughly 0.3 μas, so a micro-arcsecond-level measurement (up to 1 μas) will be required during the mission. Relative astrometry, an original and innovative technology, will enable CHES to accurately measure micro-arcsecond-level angular separation between one target star and 6–8 reference stars using laser focal planemetrology, 3 and each target star will be revisited at least 50 times ( Figure 1). In other words, CHES will be able to detect planets that transit missions (such as Transiting Exoplanet Survey Satellite or Planetary Transits and Oscillations of Stars) can not. CHES can also directly measure the real mass of a planet, which plays a crucial role in determining whether the planet may resemble Earth. Furthermore, the transit method only obtains the radius of planets and cannot directly measure planetary mass.Ĭompared with transit missions, which can only detect planets that have orbits aligned with the line of sight of the observer, the most distinct advantage of CHES is that astrometry can detect every likely planet around nearby stars, meaning it is capable of carrying out a comprehensive census on planets in neighboring planetary systems with solar analogs (FGK stars). However, the probability of such a scenario is very low (∼0.5% for Kepler mission), and the report of planetary candidates will need extensive confirmation by other approaches (eg, the radial velocity). Numerous exoplanets have been discovered using the transit method, the principle of which is that when a planet with an edge-on orbit passes in front of stars, the brightness of each host star will be periodically dimmed due to the orbit of the planet. The Kepler space telescope and the Transiting Exoplanet Survey Satellite hunt for and characterize planets using the transit method, and future programs like the Planetary Transits and Oscillations of Stars are set to do the same. Thus, the major scientific objective of CHES is to detect and characterize habitable-zone Earth-like planets orbiting 100 FGK stars among the solar system’s nearest neighbors (∼10 pc). Among the terrestrial planets, rocky planets in habitable zones orbiting nearby solar analogs are particularly eye catching, both in the field of planetary science and to the public, because a real Earth twin has not been discovered so far. 2 Unlike their siblings in our solar system, these planets are classified into hot Jupiters, warm Neptunes, super Earths, terrestrial planets, and other categories based on their orbits and masses. 1 A statistical study on a large population of exoplanets revealed that their planetary systems are complex and diverse. CHES: An astrometry mission hunting for nearby habitable planetsĪs of today, more than 5000 exoplanets have been reported since the first planet orbiting a main-sequence star was discovered. ![]()
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